These extensions already landed in master and ghc-8.10 branch:
  * CUSKs
  * ImportQualifiedPost
  * StandaloneKindSignatures
  * UnliftedNewtypes

Please see also:
  * https://gitlab.haskell.org/ghc/ghc/blob/master/docs/users_guide/8.10.1-notes.rst
  * https://gitlab.haskell.org/ghc/ghc/blob/master/testsuite/tests/driver/T4437.hs